Radio Frequency (RF) power amplifiers are commonly used in radio transmitters and transceivers to amplify radio signals. For example, a typical RF power amplifier receives signals from an exciter (e.g, a carrier frequency generator), amplifies the signals, and transfers the amplified signals to an antenna or other RF load. Many conventional radio transmitters include automatic control systems that regulate RF output power to prevent amplifier damage. Some examples of potential sources of amplifier damage include antenna load mismatch, excessive supply voltage, and excessive operating temperature. These automatic control systems typically regulate output power during normal operating conditions and protect the RF power amplifier during abnormal operating conditions using negative feedback and threshold conditions. The threshold conditions may be used to sufficiently regulate output power during abnormal operating conditions but tend to overly limit the output power during normal operating conditions.
Alternative techniques have been implemented to prevent amplifier damage. In one example, a current reference circuit is implemented with the RF power amplifier, and the current supplied to the current reference circuit is compared with a current supplied to an output stage of the RF power amplifier. To avoid dissipating a substantially large amount of power in the RF power amplifier, a relatively large ratio of the resistor associated with the output stage to the resistor associated with the current reference circuit may be selected. With this configuration, the current supplied to the current reference circuit depends on the absolute value of the resistor associated therewith. In practice, variations in ambient temperature and process errors may contribute to variations in this absolute value which in turn add error to any current measurements. External resistors (e.g., non-integrated with the RF power amplifier) may be used but can increase device costs and complexity.
Accordingly, a circuit is desired for protecting an RF power amplifier from extreme voltage or current conditions while allowing the RF power amplifier to achieve maximum output power under normal operating conditions. In addition, an RF power amplifier is desired that is protected from extreme voltage or current conditions and achieves maximum output power under normal operating conditions. In addition, a method of protecting RF power amplifiers from extreme voltage or current conditions is desired. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.